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ARTIFICIAL MUSCLE (with emphasis on Electroactive Polymers) PowerPoint Presentation
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ARTIFICIAL MUSCLE (with emphasis on Electroactive Polymers)

ARTIFICIAL MUSCLE (with emphasis on Electroactive Polymers)

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ARTIFICIAL MUSCLE (with emphasis on Electroactive Polymers)

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  1. ARTIFICIAL MUSCLE(with emphasis on Electroactive Polymers) By Bharath Ramaswamy Department of Electrical & Computer Engineering Utah State University ECE 5320: Mechatronics

  2. Introduction • Artificial Muscles are synthetic materials that behave like biological muscles. • Active materials have shown to behave macroscopically similar to some of the processes taking place in biological muscle fibers. • Artificial muscles are made up of materials which dramatically swell and shrink under chemical and/or electrical stimuli. • Eventually, artificial muscles can be "packaged into virtually any shape or size” and muscle for use in human applications could become a reality. Ref:

  3. Artificial vs. Natural muscle • Artificial actuators cannot and should not be exactly like natural muscle in all aspects. • power source • environmental conditions • materials and microstructure • response to stimulation • Fatigue • Actuators should reproduce only those characteristics of muscle that are beneficial for the application. Ref:

  4. Basic Principle • Bundles of fibers made from polymer gels would shrink when immersed in acidic solution, then swell significantly with addition of a base to the immersion solution. • Immersed in acid solution, negative ions of the polymer were attracted to positive ions from the acid that permeated the gel, which resulted in contraction. • Immersed in alkaline solution, the gel's negative ions were repulsed by negative ions from the solution, causing the polymer to expand. • The mechanical effect was similar to the action of natural muscle tissue. • In addition to exposing polymer gels to specific solutions to cause them to flex and contract, passing an electric current through a material can induce a similar effect. Ref:

  5. Enhancing Polymer Response • Electron bombardment enhances polymer response by altering the materials molecular conformation and created new chemical bonds. • It inserts defects into the material, making it more compliant and flexible. The process also increases the material's dielectric constant. • By infusing polymer gel with electrorheological fluid (ERF), which stiffens to a solid in response to an electric field the polymer’s response time to electric impulses was quickened from 3 seconds to 100 milliseconds. Ref:

  6. Increasing Strength • Fibers heated to 4500°F to form cross-links and boiled in sodium hydroxide to make them elastic. This process binds the fiber within a gelatinous mass. The mass is then encapsulated in latex and bathed in water. The ionic-polymer fibers, encased within the latex shield, are bathed in a chemical solution and contract or expand in response to changes in the solution's pH. • Adding sodium hydroxide or another base causes the fibers to stretch to as much as twice their original length. Acid results in the fibers contracting nearly as fast as human muscles and with twice the strength. • Use of computer-controlled pumps that regulate the flow of acid and base into the muscle make it possible to regulate and program the muscle's activity. Ref:

  7. Important Actuator Characteristics • Energy (the most fundamental) • Energy density • Energy efficiency • Speed of response • Force vs. Stroke • Environmental Tolerance • Power Supply Requirements • Reliability and Robustness • Passive or open-loop characteristics • Elasticity • Energy absorption: motor and a brake • Perturbation response: “preflex” • Back-drivability Ref:

  8. Requirements of Material • High dielectric constant, or ability to resist the flow of electric charge • Elasticity and Non-linear behavior • Large Displacement Response • Low Density • Large Strain Capability

  9. Terminology • Electrostriction - the non-linear reaction of ferroelectric EAP • EAP - general term describing polymers that respond to electrical stimulation • Electronic EAP - polymer that change shape or dimensions due to migration of electrons in response to electric field (usually dry) • Ionic EAP - polymer that change shape or dimensions due to migration of ions in response to electric field (usually wet and contains electrolyte) • Longitudinal EAP - polymer that responds with change in length • Bending EAP - polymer that responds with bending Ref:

  10. Materials • Ionic polymer-Metal Composites (IPMC) • Shape Memory Alloys (SMA) • Electroactive Ceramics (EAC) • Electroactive Polymers (EAP) • Rubber • Carbon Nanotubes Ref:

  11. Materials (contd.) • Ionic EAP • Ionic Gels (IGL) • Ionic Polymer-Metal Composites (IPMC) • Conductive Polymers (CP) • Electrorheological fluids (ERF) • Electronic EAP • Ferroelectric polymers • Dielectric EAP or ESSP • Electrostrictive Graft Elastomers • Liquid Crystal Elastomers Ref:

  12.  Property Electroactive Polymers (EAP) Shape Memory Alloys (SMA) Electroactive Ceramics (EAC) Actuation displacement >10% <8% short fatigue life 0.1 - 0.3 % Force (MPa) 0.1 - 3 about 700 30-40 Reaction speed m sec to sec sec to min m sec to sec Density 1- 2.5 g/cc 5 - 6 g/cc 6-8 g/cc Drive voltage 4 - 7 V NA 50 - 800 V Power consumption m-watts watts watts Fracture toughness resilient, elastic elastic fragile Comparison of Properties

  13. Electroactive Polymer ArtificialMuscle (EPAM) • Electroactive polymers are plastics that expand or contract in the presence of an electric field. Ref:

  14. Basic components of an EAP-driven system

  15. Muscle vs. Artificial Muscle Ref:

  16. Muscle vs. Artificial Muscle Ref:

  17. Sources of Excitation • Pneumatic (ex. McKibben muscle actuators) • Hydraulic (Electrorhological fluids) • Heat (Shape Memory Alloys) • Chemical • Electrical

  18. Challenges to EAP • Force actuation and mechanical energy density of EAPs are relatively low limiting the potential applications • Low Response • High Voltages required for Actuation • No effective and robust EAP material is currently available commercially. • No established database that documents the properties of the existing EAP materials.

  19. EAP Infrastructure & Areas needing attention Ref:

  20. A note on Carbon Nanotubes • Described as an extended buckminsterfullerene molecule, or "buckyball," the spherical molecule constructed solely from 60 carbon atoms. • Composed entirely of carbon atoms and, because of their molecule structure, provide exceptional strength. • Provide higher work densities per cycle • Energy needed for the nanotube actuator is a full order of magnitude lower than that of polymer gel Ref:

  21. Applications • Balloon used to cushion the deployment of the Mars Pathfinder • Inflatable telescopes • Biomimetic robots - highly maneuverable, noiseless and agile, with various shapes to emulate capabilities of terrestrial creatures with integrated multidisciplinary capabilities like soft-landing, hopping, digging and operating cooperatively. • Prosthetic Limbs • Artificial sphincters for treatment of incontinence • Method for encasing the heart with synthetic muscle in lieu of transplant procedures

  22. References • SRI International • • Konkuk University, Artificial Structures & Materials lab • • Ionic Polymer-Metal Composites (IPMC) As Biomimetic Sensors, Actuators & Artificial Muscles - A Review, M. Shahinpoor(a), Y. Bar-Cohen(b), J.O. Simpson(c) and J. Smith • • Electroactive Polymers (EAP) Low Mass Muscle Actuators, Y. Bar-Cohena, T. Xuea, B. Joffea, S.-S. Liha, M. Shahinpoorb, J. Simpsonc, J. Smithc, and P. Willisa • Electroactive Polymers As Artificial Muscles - Capabilities, Potentials And Challenges, Yoseph Bar-Cohen1 •